At the height of the McCarthyite hysteria of the 1950s, John Paton Davies, Jr., was summoned to the State Department one morning and fired. His offense? The career diplomat had counseled the U.S. government during World War II that the Communist forces in China were poised to take over the country—which they did, in 1949. Davies joined the thousands of others who became the victims of a political maelstrom that engulfed the country and deprived the United States of the wisdom and...